Color shifting coatings are well known and can be found on some United States banknotes and on banknotes of many other countries. Although printed or hot stamped diffractive structures are color changing and are sometimes said to be color shifting, this invention relates primarily a color shift that occurs through thin film interference effects; that is, from multilayered thin film coatings having a reflector, a spacer and an absorber or a stack of interference layers. U.S. Pat. Nos. 6,236,510, 5,570,847, and 5,279,657 are some exemplary patents in the name of Roger Phillips where thin film interference flakes are disclosed. U.S. Pat. Nos. 7,258,900, 7,047,883 and 7,517,578 in the name of Raksha et al. disclose magnetically alignable thin film pigment flakes and methods of aligning such flakes. All of the abovementioned patents and applications are incorporated herein by reference, for all purposes.
United States patent application US 20080069979, incorporated herein by reference, entitled “Security image coated with a single coating having visually distinct regions” discloses a security image which is formed from flakes having a first color with flakes having a second different color mixed within a carrier uniformly. The flakes having the second color are magnetically orientable and the flakes having the first color are non-magnetic and do not align or orient in a magnetic field. By exposing at least a single coated region to a magnetic field that is substantially orthogonal to the substrate upon which the coating of flakes is coated, a visible region having the first color is provided as the magnetic flakes are upstanding and the non-magnetic flakes are lying flat upon the substrate. In another region where there is no magnetic field applied, a visible region having a third perceived color that is different from the first color or the second color seen. Although interesting effects are provided using this method, the instant invention affords a flexibility in which way the coating is viewed or from where the incident light is located.
This invention takes advantage of the fact that magnetic and non-magnetically oriented flakes behave differently in the presence of a magnetic field. Furthermore carefully selecting goniochromatic characteristics of the flakes and the angle of the magnetic field, yields a very useful security coating which exhibits a color shift when tilted from East to West or North to South; and wherein the security coating exhibits a different color when tilted from East to West or North to South, and wherein the same color is exhibited when the coating is viewed at normal angle.
It is an object of this invention to produce a coating that has two different color shifting effects when observed from two different directions and the same color when observed at normal angle.
It is an object of this invention to produce a color shift between a first and second color when tilted about a first axis, and that produces a color shift from the first to a third color when tilted about an axis orthogonal to the first axis, wherein the first, second and third colors are three visually distinguishable different colors.
It is a further object of this invention to use a mixture of magnetically oriented magnetic color shifting flakes and non-magnetic non-oriented color shifting flakes wherein a color of the flakes is the same at normal incidence.
It is a further object of this invention to use a mixture of only two different flake types arranged and fixed in a particular orientation upon a substrate, to yield a color shift from a first to a second color, or from the first to a third color depending upon the tilt of the substrate.